Apparatus for adjusting the natural frequency of rotating equpment



Aug. 13, 1968 M BERMAN APPARATUS FOR ADJUSTING THE NATURAL FREQUENCY OF ROTATING EQUIPMENT Filed Nov. 7, 1966 FIGJ MERRIL BERMAN BY %aMLJ/\/.M;

United States Patent 3,396,665 APPARATUS FOR ADJUSTING THE NATURAL FREQUENCY OF ROTATING EQUIPMENT Merril Berman, Denver, Colo., assignor to Harrworth,

Inc., a corporation of Delaware Filed Nov. 7, 1966, Ser. No. 592,428 9 Claims. (Cl. 103-87) ABSTRACT OF THE DISCLOSURE A frequency adjusting coupling means which joins standard components of a drive system at locations either spaced or offset from the normal connecting points of these components. The use of the frequency coupling means alters the rigidity of the connection between the components joined thereby and this change in rigidity alters the natural frequency of the entire drive system.

Brief summary of the invention This invention relates to means for adjusting the natural frequency of apparatus comprising a mechanical driving means and, particularly, to means for altering the natural frequency of apparatus driven by vertically disposed driving means, such as a vertical pump.

The natural frequency of a vertical pump is dependent on the various components which make up the pump and the method by which the components are joined. Because of the almost infinite number of elements which can be combined to form a vertical pump assembly it is nearly impossible to accurately predict the natural frequency of a pump until the pump is actually fabricated, assembled, and installed.

Due to the unpredictability of the natural frequency it often happens that after a pump is assembled and tested the natural frequency is found to coincide with, or be close to, the operating speed of the pump. This occurrence produces high vibrational amplitudes in the pump assembly which seriously impair the pump performance and, if not corrected, will shorten the service life of the pump.

When this coincidence of operating speed and resonant frequency occurs it is necessary to alter the natural frequency of the pump. Heretofore this was accomplished by redesign or substitution of pump components, or by changing the materials from which the major pump components were fabricated; methods which were time consuming and costly. The use of elastomeric vibration dampers in these situations also proved unsatisfactory since the service life of the elastomeric materials used in these applications was relatively short lived.

Therefore, it is an object of this invention to provide a means for adjusting the natural frequency of apparatus comprising driving means without requiring extensive modification of the apparatus.

It is another object of the invention to provide a means for adjusting the natural frequency of a vertically disposed drive apparatus without replacing or altering major components of the apparatus.

It is a further object of this invention to provide an apparatus for altering the natural frequency of a drive apparatus by means of inserting simple structural members.

Yet, another object of the invention is to provide a means for altering the natural frequency of a vertically disposed drive apparatus by means other than the addition to the apparatus of an elastomeric dampening component.

A further object of the invention is to provide an easily installed apparatus for altering the natural frequency of vertically disposed drive machinery.

Yet, another object of the invention is to provide an apparatus for altering the natural frequency of the vertically disposed drive system which apparatus will have the 3,396,665 Patented Aug. 13, 1968 durability of a structural component of the drive system.

To accomplish these objects the invention provides a frequency adjusting coupling means which joins standard components of a drive system at locations either spaced or offset from the normal connecting points of these components. The use of the frequency adjusting coupling means alters the rigidity of the connection between the components joined thereby, and this change in rigidity alters the natural frequency of the entire drive system.

Various other objects and advantages will be apparent from the following description of several embodiments of the invention and the novel features will be particularly pointed out hereinafter in connection with the appended claims.

Brief description of the drawings In the accompanying drawings: FIGURE 1 shows a side elevation of a vertical pum drive motor unit and pumping unit embodying the invention.

FIGURE 2 is an exploded view in vertical section showing the frequency adjusting members incorporated in FIG- URE 1.

FIGURE 3 is a top view of the upper frequency adjusting member shown in FIGURE 2.

FIGURE 4 is an exploded view in vertical section showing another embodiment of the invention.

FIGURE 5 is a top view of the upper frequency adjusting member shown in FIGURE 4.

FIGURE 1 shows a vertical pump assembly 10 having a drive motor 12 mounted within a drive motor housing 14 forming a drive motor unit 16. A drive shaft 18 extends from the drive motor to the pump works 20 which are housed within the pump casing 22.

As shown in FIGURE 2, the end face 32 of drive motor housing 14 is adapted to mate with the end face 34 of pump casing 22 as is standard practice in connecting adjacent parts in mechanical assemblies. End faces 32 and 34 respectively have a plurality of bolting holes 36 and 38 respectively adapted to receive bolting means to connect the drive motor housing to the pump casing. Additionally, the drive motor housing and pump casing end faces have passages 40 and 42 respectively to provide clearance for the drive shaft 18. Passage 40 in the drive motor housing has a counterbore 44 adapted to cooperate with the raised shoulder 46 on the end face of the pump casing to align the pump casing with the drive motor housing during assembly of the two parts.

Installed between and connecting the drive motor housing 14 and the pump casing 22 is the proposed invention, a frequency adjusting coupling means 23. The coupling means 23 comprises, first and second frequency adjusting members 24 and 26 respectively which are connected to each other by a plurality of nuts 28 and bolts 30.

The first frequency adjusting member 24 is composed of an annular base portion 48 and a flanged portion 50 extending radially outward therefrom. A raised shoulder 52 is adapted to engage with counterbore 44 on the end face 32 of the drive motor housing. A plurality of threaded bores 54 are located in the upper bearing surface 56 of the annular portion 48 in positions which correspond to the location of bolt holes 36 in the end face of the drive motor housing. First frequency adjusting member 24 is connected to end face 32 of the drive motor housing by means of bolts 58 which extend through bolting holes 36 and engage the threaded bores 54.

In the same manner, the second frequency adjusting member 26 has an annular base portion 60 and a flange section 62 extending radially outward therefrom, and a plurality of threaded bores 64 in the lower bearing surface 66 of annular base portion 60. The second frequency adjusting member has a counterbore 68 in the annular base portion corresponding to counterbore 44 in the end face 32 of drive motor housing 14 to engage with the shoulder 46 on end face 34 of the pump casing, to align the second frequency adjusting member with the pump casing during assembly of the two parts.

The second frequency adjusting member 26 is connected to the pump casing 22 by means of bolts 70 which pass through bolt holes 38 in end face 34 of the pump casing and engage the threaded bores 64 in the base portion 60 of the second frequency adjusting member.

The flanged portions 50 and 62 of the first and second frequency adjusting members respectively are connected by a plurality of bolts 28 and nuts 30. Bolting holes 72 and 74 on flanged portions 50 and 62 respectively are correspondingly disposed on their respective flanged portions at equal angular spacings and at a constant radial distance from the center of the frequency adjusting memher.

As seen in the drawings, the radial distance to the bolting holes 72 and 74 respectively on the first and second frequency adjusting members 24 and 26 is greater than the radial distance to the bolting holes 36 and 38 respectively on the pump casing and the motor housing. This difference in distance combined with the relative thinness of the flanged sections 50 and 62 results in a joint between the first and second frequency adjusting means which is significantly less rigid than the normal connection between the motor housing 14 and the pump casing 22. This difference in rigidity produces a change in the natural frequency of the entire pumping unit.

Under certain circumstances it may be inconvenient or not possible to install frequency adjusting members with radially outward extending flange sections as shown in FIGURES 1 through 3. For example, such installations may be diflicult where space is at a premium. Under such circumstances frequency adjusting members with flanged portions extending radially inward would be more suitable. They would provide the same ability to adjust the natural frequency without significantly affecting the space requirements for the pumping system.

Shown in FIGURE 4 is another embodiment of the present invention including frequency adjusting members having inwardly protruding flange sections. In order to avoid unnecessary numbering and confusion objects shown in FIGURE 4 which correspond to those shown in FIGURE 2 will be similarly numbered.

Accordingly, a first frequency adjusting member 100 is composed of an annular base portion 102 having a flanged portion consisting of four radially inward protruding members each designated 104, the bearing surface 106 has -a raised shoulder 108 adapted to engage counterbore 44 in end face 32 of the drive motor housing. Threaded bores 110 on bearing surface 106 receive and engage bolts 58 passing through bolt holes 36 in the drive motor housing to connect the first frequency adjusting member to said housing. Towards the radially innermost end of each of flange member 104, is a bolt hole 112 which will be used for connecting the first and second frequency adjusting members to each other.

Similarly, the second frequency adjusting member 114 has an annular base portion 116 with a bearing surface 118 adjacent end face 34 of the pump casing. Threaded bores 120 on bearing surface 118 are disposed in correspondence with bolt holes 38 on the end face of the pump casing to receive and engage bolts 70, thereby connecting the second frequency adjusting member to the pump casing. Counterbore 122 in bearing surface 118 engages raised shoulder 46 of the pump casing to align the second frequency adjusting member with the pump casing When the two are assembled. The flanged portion of the second frequency adjusting member is composed similarly to that of the first frequency adjusting member, consisting of four radially inward protruding members 124 each of which having a bolt hole 126, corresponding to bolt holes 112 in the first frequency adjusting member.

The first and second frequency adjusting members are connected by means of bolts 128 and nuts 130 passing through bolt holes 112 and 126. Again, because of the thinness of flange sections 104 and 134, and the distance between the points of connection of the frequency adjusting members to each other and to the drive motor housing and pump casing, the rigidity of the joint with the frequency adjusting members is greatly reduced from that of the normal connection between the drive motor housing and the pump casing.

A typical practical application of the subject invention would be where a pump has been installed and a coincidence has been found between the pump operating speed and natural frequency. In that case, the drive motor unit would then be disconnected from the pump casing and the frequency adjusting members installed. After connecting the frequency adjusting members to the pump casing and the drive motor housing, the members would be coupled to each other and the pump then retested for the level of vibration at operating speeds. If the frequency of the pump has not been sufiiciently altered, adjustments can be made by way of reducing the amount of material in the flange portion of the frequency adjusting means, or altering the location of bolting holes on the flange portions thereof.

Further, the flanged portion need not be circular or symmetrical as shown in the embodiments described herein but can be of any configuration found satisfactory.

Of course, the frequency adjusting members need not be used only for vertical pumps having a drive unit above and mounted upon the pump casing, but can be used for vertical pumps where the drive unit is fully submerged and depending from the pump casing. Furthermore, this system need not be used solely for vertical apparatus but could also be effectively employed in horizontally disposed apparatus.

It will be understood that various changes in the details, materials, and arrangements of parts which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention, as expressed in the appendent claims.

What is claimed is:

1. Means for altering the natural frequency of a drive system comprising:

(a) an electric drive means;

(b) a driven means connected to the drive means;

(c) a housing for the drive means;

(d) a casing for the driven means adapted to be connected to the housing;

(e) a first frequency adjusting member connected to the housing for the drive means;

(f) a second frequency adjusting member connected to the casing for the driven means; and

(g) means to connect the first and second frequency adjusting members, the disposition of said connecting means being radially and circumferentially variable so that change of the location of the connecting means will effect a change in the rigidity of the connection between the first and second frequency adjusting members and thereby alter the natural frequency of the drive system.

2. The combination claimed in claim 1 wherein:

(a) the first frequency adjusting member is secured to the housing at a plurality of distinct points;

(b) the second frequency adjusting member is secured to the casing at a plurality of distinct points;

(c) the first and second frequency adjusting members are connected at a plurality of distinct points out of alignment with the points at which the first and the second frequency adjusting members respectively are secured to the housing and the casing.

3. The combination claimed in claim 2 wherein at least one of the first and second frequency adjusting members is disposed inter-mediate the housing and the casing.

4. The combination claimed in claim 2 further comprising:

(a) drive shaft means connecting the drive means to the driven means; and

(b) wherein the plurality of points at which the first and second frequency adjusting members are connected are spaced equi-distant from the axis of the drive shaft means at a distance greater than the distance from the axis of the drive shaft means to each of the points at which the first frequency adjusting member is connected to the housing.

5. The combination claimed in claim 2 further compris- (a) drive shaft means connecting the drive means to the driven means; and

(b) wherein the plurality of points at which the first and second frequency adjusting members are connected are spaced equidistant from the axis of the drive shaft means at a distance less than the distance from the axis of the drive shaft means to each of the points at which the first frequency adjusting member is connected to the housing.

6. In a vertical pump, the combination for altering the natural frequency of the pump comprising:

(a) a vertically disposed pump casing;

(b) an electric drive motor unit in spaced relation to the pump casing co-axially disposed therewith;

(c) pumping means disposed within the pump casing;

(d) a drive shaft extending from the drive motor unit to the pump means to drive the pump means;

(e) means adapted for connecting the drive motor unit to the pump casing disposed on the adjacent ends of the drive motor unit and the pump casing;

(f) a first frequency adjusting member connected to the end of the drive motor unit adjacent the pump casing;

(g) a second frequency adjusting member connected to the end of the pump casing adjacent the drive motor unit;

(h) means to connect the first and second frequency adjusting members, the disposition of said connecting means being radially and circumferentially variable so that change of the location of the connecting means will effect a change in the rigidity of the connection between the first and second frequency adjusting members and thereby alter the natural frequency of the pump.

7. The combination claimed in claim 6 wherein the first and second frequency adjusting members each comprise:

(a) an annular base portion;

(b) a flange portion continuous with the base portion;

(c) a plurality of fastening means disposed on the flange portion adapted for connecting the first and second frequency adjusting members;

(d) a plurality of fastening means disposed on the annular base portion adapted to cooperate with the means for connecting the drive motor unit to the pump casing disposed on the adjacent ends of the drive motor unit and the pump casing.

8. The combination claimed in claim 7 wherein:

(a) the flange portion of each of the first and second frequency adjusting members comprises an annular disk extending radially outward from the annular base portion thereof; and

(b) the plurality of fastening means disposed on the flange portion are disposed at a greater distance from the center of the annular base portion than are the fastening means disposed on the annular base portion thereof.

9. The combination claimed in claim 7 wherein:

(a) the flange portion of each of the first and second frequency adjusting members comprises a plurality of fingers extending radially inward from the annular base portion thereof; and

(b) the plurality of fastening means disposed on the flange portion are disposed at a lesser distance from the center of the annular base portion than are the fastening means disposed on the annular base portion thereof.

References Cited UNITED STATES PATENTS 2,421,529 6/1947 Tyler 248- 20 2,459,036 1/1949 Lipe et al. 24s 20 2,610,017 9/1952 Lambert et al 24s 21 2,958,296 11/1960 Carter 103-21-s 2,891,746 6/1959 Pesel 24s 15 HENRY F. RADUAZO, Primary Examiner. 

